For heating a large annular component (for example, in the shrink fit process of a bearing, a large bearing is required to be heated), the oil bath heating, the electromagnetic induction heating via an eddy current, and the air heating are methods commonly used. Among the above heating methods, the air heating is mostly used. Taking an air heating furnace used in the shrink fit process of the bearing as an example, the air heating furnace takes hot air as a heat transfer medium, to heat a surface of a shrink fit bearing component, and the heating method is mainly the convective heat transfer, which is supplemented by the radiation heat transfer.
As shown in FIG. 1, FIG. 1 is a schematic view showing the structure of an air heating furnace in the conventional technology, and FIG. 1 shows the structure of a typical heating furnace used for shrink fit of the bearing component used in the present industries. The air heating furnace includes an upper part and a lower part, namely a furnace lid 81a and a furnace base 82. In the conventional technology, a heating furnace body is formed by welding a sectional steel and a steel plate, engineering material with heat insulation property (rock wool of aluminum silicate fiber, etc.) is filled between a furnace flue and a protective shell through tiling and overlapping to be used as a furnace liner for heat insulation. A furnace motor 83 is provided at a center position at the top of the furnace lid 81, the motor is fixed via a flange, and the furnace motor drives a centrifugal fan 86 to provide power for circulation and flowing of air. A flow guiding plate is provided below the centrifugal fan 86, and the flow guiding plate and an inner wall of the furnace lid 81 form a radial flow channel part of an upper air flow passage. An annular lower flow guiding plate 85, which is coaxial with a vertical portion of the upper flowing guiding plate, is provided in the furnace base 82, and after the furnace lid 81 and the furnace base 82 are engaged, the upper flow guiding plate 84 and the lower flow guiding plate 85 can abut against each other inside the heating furnace to form an annular air flow passage. A channel beam is adopted as a base frame of the furnace base 82, to enhance the uniformity of a temperature of the furnace. Gaps with uniform heights are arranged between the lower flow guiding plate 85 and an inner wall of the furnace base 82, to allow air flow coming from the furnace lid 81 to pass through an annular gap to enter an area where the heated bearing component is located via the gaps with uniform heights of the furnace base 82 (as shown by arrows in FIG. 1). In an annular area encircled by the upper flow guiding plate 84 and the lower flow guiding plate 85, the air flow is converged to a suction port of the centrifugal fan 86 after releasing heat to the surface of the bearing component. Generally, a certain number of electric heating elements are provided in the radial flow channel in the furnace lid 81 as heaters 87 to heat the air flow, and the electric heating elements are uniformly distributed along a periphery of the radial flow channel. The heated large bearing component is supported by multiple points to be placed on the furnace base 82, and coaxial with the lower flow guiding plate 85, and is equally spaced from the lower flow guiding plate 85.
A basic structure of the air heating furnace in the conventional technology is described above, and in the process of carrying out the present application, the inventor found that the air heating furnace in the conventional technology has the following disadvantages:
1. There is waste in the air flow passage.
With the increase of a radial dimension of the bearing, the space of a center area within an annular area of the bearing component may increase as well, and in the case that the radial dimension of the bearing increases to an order magnitude of several meters, when such a bearing component is heated, the air in the space of the center area does not participate in the convective heat exchange between the surface of the bearing and the hot air, therefore there is huge waste in the air flow passage. Also, with the increase of the dimension of the bearing, for allowing the air flow to fully flow, the power of a drive motor of a fan is required to increase accordingly, and a power consumption increases as well.
2. There is waste in material for manufacturing the heating device.
Viewed from an axial direction of the heating furnace of a cylinder shape, the material used in center areas of the furnace lid 81 and the furnace base 82 is not necessary, especially the heat insulation material used in these areas. Also, due to the increase of the overall structure, for ensuring the strength, the dimension of a main beam structure of the furnace body may be increased, and the material consumed may be further increased, thus sharply increasing the manufacturing cost.
3. There is a warping problem after the heating furnace being heated via an eddy current.
The bearing with a large dimension has a large diameter and a large mass (greater than several tons), and a warping problem caused by non-uniform heating may occur to the bearing after the bearing being heated via the eddy current, thus a good assembling quality cannot be assured. In addition, due to remnant magnetism in the component with a large dimension, the component cannot be normally used in a subsequent long term.
4. Transportation is limited due to the increase of dimension of the heating furnace.
The structural dimension of the furnace body is limited, and a structural dimension of the space in the furnace body of a traditional hot air flow heating furnace increases with the increase of the radial dimension of a heated annular work piece (large bearing), resulting in an increase of the manufacturing cost; and the transportation of the heating furnace with an oversize width is restricted.
5. There are hidden risks in health and safety in the hot oil bathing heating method.
The traditional bearing heating method of hot oil bathing has health and safety problems (fire risk exists), furthermore, issues of dealing with the environment and the oil should also be considered, thus the cost is high; the bearing is apt to be contaminated, and a new bearing may destroy a protective oil.